1. Field of the Invention
The present invention generally relates to a disc cartridge of a generally rectangular configuration for removably accommodating a disc-shaped optical or magnetooptical recording medium and, more particularly, to a lid structure for the disc cartridge for selectively opening and closing the access opening leading into the interior of the disc cartridge for removal or replacement of the optical recording medium.
2. Description of the Prior Art
The disc cartridge of the type referred to above is disclosed in, for example, the Japanese Laid-open Patent Publication No. 5-243626, published in 1994. According to this publication, the disc cartridge comprises a generally rectangular flattened casing having an access opening defined at a rear end thereof so as to extend over the entire width thereof. This known disc cartridge also includes a lid for selectively opening and closing the access opening to allow the disc-shaped recording medium, for example, the optical disc, to be removed from and inserted into the interior of the casing, respectively. The lid has a flange that can be received within the access opening in the casing when it is held in position to close the access opening. This lid is pivoted at one end to one corner region at the rear end of the casing so that it can be swung about 180.degree. to open the access opening.
In this known disc cartridge, problems would arise when detent recesses that may be utilized for positioning the disc cartridge or for removal of one disc cartridge from a library are to be defined in the disc cartridge at respective locations lying on the path of movement of the optical disc out from or into the casing. As is well known to those skilled in the art, the cartridge casing has a width slightly greater than the outer diameter of the optical disc and, therefore, if the detent recesses are formed in opposite side walls of the cartridge casing, the detent recesses would leave an internal space therebetween which is narrower than the outer diameter of the optical disc. Accordingly, where the detent recesses are to be formed, the cartridge casing must have an increased width in order for the optical disc to be smoothly removed from or inserted into the cartridge casing. Thus, formation of the detent recesses in the cartridge casing inevitably results in increase in size of the disc cartridge.
The increase in size of the disc cartridge may be avoided if a wall element defining each detent recess in the respective side wall of the cartridge casing is formed with a slit that is so sized and so shaped as to allow opposite outer peripheral portions of the optical disc to pass through the associated slits during removal or insertion of the optical disc from or into the cartridge casing. The use of the slits in the wall elements defining the respective detent recesses in turn necessitates the lid to be so shaped and so configured as to have, in addition to the capability of selectively opening and closing the access opening, an extra capability of selectively opening and closing the slits to thereby avoid any possible ingress of foreign matter into the cartridge casing. Specifically, a space between the optical disc and the access opening is necessarily occupied by the lid having a thickness generally equal to the space between top and bottom panels forming the cartridge casing. The lid having such an increased wall thickness is susceptible to deformation during molding thereof and, for example, the accuracy with which a partially arcuate regulating surface used to restrict an arbitrary motion or play of the optical disc within the cartridge casing is formed tends to be lowered. In addition, an increased amount of synthetic resin is needed to form the lid, accompanied by increase in manufacturing cost and weight.
Moreover, so long as the single lid is used to selectively open and close the access opening, no optical disc can be smoothly removed from or inserted into the disc cartridge unless the lid is fully swung 180.degree. or more to thereby clear the path of movement of the optical disc from or into the disc cartridge. This means that the prior art disc cartridge requires the lid to have an increased stroke of pivotal movement between opened and closed positions. This means that removal or insertion of the optical disc from or into the disc cartridge in a limited available space would not be accomplished with no difficulty. In addition, the necessity of the lid to pivot relative to the cartridge casing requires a gap present between a pivot front end of the flange and a cutout opening, and foreign matter can easily find a way into the disc cartridge through such gap.